New regulations have been established to protect the stratospheric ozone layer from possible damage by fully halogenated chlorofluorocarbons (CFCs). 1,1-Difluoroethane (CHF.sub.2 CH.sub.3 or HFC-152a) is a non-chlorine containing fluorocarbon that is especially valuable as a refrigerant, blowing agent, propellant, and chemical intermediate for manufacture of vinyl fluoride, among other uses.
1,1-Difluoroethane may be prepared by reacting vinyl chloride with hydrogen fluoride in the presence of a catalyst such as a palladium, vanadium, tin, or other catalysts. The reaction product from such processes typically contains, in addition to the desired 1,1-difluoroethane, unreacted vinyl chloride and hydrogen fluoride, by-product hydrogen chloride and small amounts of organic by-products such as 1-chloro-1-fluoroethane and vinyl fluoride. While the majority of these impurities can be removed by conventional distillation, vinyl chloride is very difficult to separate from 1,1-difluoroethane when the 1,1-difluoroethane concentration is above about 85 mole %. Depending on the temperature, vinyl chloride and 1,1-difluoroethane in these concentrations form either an azeotrope or azeotrope-like composition, making purification of 1,1-difluoroethane by conventional distillation difficult or impossible.
The presence of even relatively small amounts of vinyl chloride in the 1,1-difluoroethane product is undesirable in many applications of this product. Numerous attempts have been made to reduce the amount of vinyl chloride remaining in the 1,1-difluoroethane but these have been inadequate for achieving low levels of vinyl chloride or have been costly to operate.
The present invention solves problems associated with conventional purification methods by providing processes for removing 1,1-difluoroethane from mixtures comprising 1,1-difluoroethane and vinyl chloride which is simple and effective for obtaining low levels of vinyl chloride in the 1,1-difluoroethane product.